a) Field of the Invention
The invention relates to air-activatable polymerisable compositions and their use. The compositions are suitable for use as one-component systems for forming polymers, requiring no primers. The compositions are useful as adhesives, sealants, surface coatings, moulding resins and composite matrices, for example. These compositions are particularly suitable for use as thread-locking compounds, e.g. for cementing nuts to threaded shafts, bushes to bush housings and the like.
b) Description of the Related Art
The cure of acrylic adhesives is initiated by a two-part redox system. The first part, the initiator, is normally present in the base component of the adhesive and the second part is present in the accelerator or curative component. One widely used curative is the reaction product of aniline and n-butyraldehyde. The reaction product was first known from U.S. Pat. No. 1,780,334 assigned to E. I. Du Pont DeNemours and Co. The condensation of aniline and n-butyraldehyde results in many products, some having complex structures. However it appears that the major component and active ingredient is a substituted dihydropyridine (DHP).
An adhesive composition which can be formulated either as a two-part system or as a system utilising a primer is disclosed in U.S. Pat. No. 3,890,407, assigned to E. I. Du Pont DeNemours and Co. The composition comprises a sulphur-bearing component selected from chlorosulphonated polyethylene and a mixture of sulphonyl chloride with chlorinated polyethylene in at least one polymerisable vinyl monomer and an accelerator comprising a primary amine-aldehyde condensation product. U.S. Pat. No. 4,112,013 also of E. I. Du Pont DeNemours and Co. which was divided from U.S. Pat. No. 3,890,407 specifies that the chlorosulphonated polyethylene is made from branched polyethylene having a melt index of about 100, the chlorosulphonated polyethylene containing about 43% chlorine by weight and about 34 mmoles of sulphonyl chloride per 100 grams of polymer and the composition may also comprise a mixture of methyl-methacrylate, glacial methacrylic acid and ethyleneglycol dimethacrylate. A further U.S. Pat. No. 4,106,971, also divided from U.S. Pat. No. 3,890,407, relates to a method of bonding two surfaces comprising the above disclosed adhesive compositions.
A bonding accelerator containing a condensation reaction product of an aldehyde and a primary or secondary amine is known from U.S. Pat. No. 3,591,438, assigned to Loctite Corporation, together with a reducing activator comprising either a sulphur-containing free radical accelerator or a compound containing an oxidizable transition metal. Such a condensation reaction product is also known for use in conjunction with a polymerisable acrylate ester monomer and a peroxy polymerisation initiator (U.S. Pat. No. 3,616,040 also of Loctite Corporation). U.S. Pat. No. 4,430,480, assigned to Loctite Corporation relates to an adhesive composition which comprises a first part comprising a solution of chlorosulphonated polyethylene in at least one polymerisable vinyl monomer, a polymerisation catalyst which comprises at least one free-radical initiator and a second part comprising an activator composition which consists of at least 70% of the condensation reaction product formed between butyraldehyde and aniline.
An improved adhesive composition of this type, enriched in N-phenyl-3,5-diethyl-2-propyl-1,2-dihydropyridine to a concentration of at least about 70% by weight of the condensation reaction products is known from U.S. Pat. No. 4,430,480.
U.S. Pat. No. 4,602,073 assigned to National Starch & Chemical Corporation describes a two-part adhesive, the first part comprising a mixture of polymerisable optionally substituted acrylic monomers, a diazonium salt initiator and optionally a Lewis acid or salt as stabiliser and a second part comprising an aldehyde-amine condensation product as an activator to induce decomposition of the diazonium salt initiator in the first part.
U.S. Pat. No. 4,656,229 also assigned to National Starch & Chemical Corporation describes a similar two-part anaerobic curing adhesive composition utilising a first part comprising a mixture of free radical polymerisable optionally substituted acrylic monomers and a diaryliodonium salt initiator and a second part comprising an aldehyde-amine condensation product as an activator.
Many of the above compositions based on aldehyde-amine condensation reaction products are, however, two-part systems and suffer from the disadvantages and limitations of use associated with such systems.
An adhesive composition which is described as being polymerisable either aerobically or anaerobically is disclosed in U.S. Pat. Nos. 4,348,503, and 4,429,088 divided therefrom, of Bachmann, and comprises an acrylic ester monomer capable of free-radical polymerisation and a monomeric polyacrylate ester prepolymer together with a catalyst system which comprises an aromatic perester free-radical precursor, an organic acid and a soluble compound of a transition metal cure accelerator. However this composition requires a separate activator such as an amine-aldehyde condensate.
U.S. Pat. No. 4,452,955, assigned to Minnesota Mining and Manufacturing Company, discloses an adhesive composition comprising a polymerisable monomer having at least one alpha, beta-unsaturated carboxyl functionality and as an accelerator an organic sulphimide or perfluroalkylsulphonanilide, together with an inhibitor of free-radical polymerisation to retard polymerisation of the unsaturated carboxyl functionality on contact with the accelerator, and a condensation reaction product of an aldehyde and a primary or secondary amine.
Free radical polymerizable compositions are disclosed in European Patent Specification No. 0,356,875 of Henkel KGA. These comprise ethylenically unsaturated, polymerizable compounds together with an activator system which can be initiated by oxygen and water, comprising an N-alkyl-substituted tert-arylamine with at least one aliphatic CH bond in the alpha position, a metal compound generally used for accelerating the drying of unsaturated oil and which is at least partially soluble in the composition, and a compound of a weakly acidic carboxylic acid having a pKa value of no less than about 0.9, which can be hydrolyzed to a free carboxylic acid on contact with moisture.
The N-alkyl-substituted tert.-arylamines correspond in particular to the general formula: ##STR1## in which R.sub.1, is an optionally substituted aryl radical, more especially an optionally alkyl-substituted phenyl radical, R.sub.2, has the same meaning as R.sub.1, or is an optionally substituted, linear or branched alkyl radical and R.sub.3, is a linear or branched alkyl radical which may be substituted, but contains at least one hydrogen atom in the alpha-position to the nitrogen. These compositions depend on the action of both water and oxygen to effect a cure reaction. As such their formulations are very dependant on humidity conditions.
WO91/10687-A of Henkel KGaA discloses air-activatable adhesive compositions comprising mixtures of free-radically polymerisable unsaturated olefinic compounds, and hydrazone compounds prepared and stored under anaerobic conditions. The hydrazones may be alkyl, cycloalkyl and/or aryl hydrazone(s) of aldehyde(s) and/or ketone(s) and are claimed to react with air to form hydroperoxides useful as polymerisation initiators. The one component compositions are stable in the absence of air.
EP 0,502,733A of Loctite (Ireland) Limited (the contents of which are incorporated herein by reference) describes a one-part air-activatable polymerisable composition comprising:
(a)at least one free-radically polymerisable monomer, and PA1 (b) an activator system for effective polymerisation of the free-radically polymerisable monomer, said activator system comprising at least one auto-oxidisable compound of a formula which includes the structure I: ##STR2## where x is 0 or 1, and where the lines representing unfilled valencies indicate bonds to carbon, hydrogen or hetero atoms, PA1 alone or in combination with a weak acid; PA1 with the proviso that: PA1 when x=0, the nitrogen atom in structure I is not bonded to a PA1 second nitrogen atom: PA1 and when x=1 there is a structure I in the compound in which the ##STR3## PA1 (a) a free-radically polymerisable monomer, and an activator system for effective polymerisation of the free-radically polymerisable monomer, said activator system comprising: PA1 (b) an auto-oxidisable compound which is a dihydropyridine having a general formula selected from II: ##STR4## where R.sub.1 to R.sub.7, which may be the same or different, are independently selected from hydrogen, hydrocarbyl and heterohydrocarbyl groups, silyl groups, and substituted derivatives of any of the foregoing, and any two of the groups R.sub.1 to R.sub.7 may together form a mono- or polycyclic ring structure, which may optionally be a fused ring structure, and which in turn may be substituted, provided that none of the groups R.sub.1 to R.sub.7 is a group which is known to interfere with polymerisation, and that in the case of 1,4-dihydropyridines of formula II (iv) the groups R.sub.2 and R.sub.5 at the 3- and 5-positions are not both electron-withdrawing groups, PA1 (c) an onium salt selected from diazonium, iodonium and sulfonium salts which do not interfere with polymerisation, and PA1 (d) a soluble ionic salt, provided that the composition does not contain a peroxide, or a peroxide precursor which produces peroxide in the absence of air or any ingredient which is a significant source of radicals in the absence of air. PA1 (i) straight chain or branched linear or alicyclic aliphatic groups including alkyl, alkenyl and alkynyl, preferably containing from 1 to 20, more preferably from 1 to 10, most preferably from I to 5 carbon atoms; and alkylene and alkenylene groups forming part of a ring structure which preferably contains from 3 to 30, more preferably 5 to 20 carbon atoms; PA1 (ii) aromatic groups including aryl, alkaryl and aralkyl groups, preferably containing 6 to 20 carbon atoms, more preferably 6 to 10 carbon atoms, and optionally having a fused ring structure. PA1 a stabilised or unstabilised diazonium salt corresponding to the general formula III: EQU [Ar N=N.sup.+ ].sub.a X.sup.(-)a PA1 wherein a is an integer of 1, 2 or 3 taken so as to equalise the valence charge of the salt and Ar is an aryl or substituted aryl radical (including diazonium-substituted aryl radicals), and X is an anion; PA1 or an iodonium salt corresponding to the general formula IV: ##STR5## wherein R.sub.8 and R.sub.9, which may be the same or different, are selected from aryl or substituted aryl groups, for example, substituted with alkyl, alkoxy, alkenyl, cycloalkyl, cycloalkenyl, aryl, chloro, fluoro, bromo, iodo, and nitro groups, and X.sup.- is a monovalent anion, PA1 or a sulphonium salt corresponding to the general formula V: ##STR6## wherein R.sub.10, R.sub.11 and R.sub.12 which may be the same or different are selected from aryl or substituted aryl groups (including fused ring substituted aryl radicals) and X is a monovalent anion.
moiety does not form part of a phenyl ring;
with the proviso that the composition does not contain a peroxide, or a peroxide precursor which produces peroxide in the absence of air or any ingredient which is a significant source of radicals in the absence of air.
Preferred auto-oxidisable compounds are selected from the group consisting of partially hydrogenated pyridines, condensation products of cyclic ketones and ureas, Schiff's bases, indoles, pyrroles, imidazoles, piperazines, carbazoles, tetrahydroquinolines, and substituted derivatives thereof, particularly dihydropyridines.
The presence of a weak acid is generally preferred in order to achieve a satisfactory rate of auto-oxidation for the partially hydrogenated pyridines. The majority of the working examples using dihydropyridines in EP 92 301 899.8 have acrylic acid in the formulation. Other acids used are methacrylic acid, trichloroacetic acid, cyanoacetic acid, salicylic acid, benzoic acid, acetic acid and saccharin.
The composition may also contain a soluble ionic salt, particularly a cobalt or iron salt.
The compositions as described in EP 92 301 899.8 are stable on storage in the absence of air, are activated by exposure to air, and will then cure in either the presence or absence of air. However the use of volatile acids, particularly acrylic acid, may give rise to odour problems in a working environment.
DD 287 796 A6 describes a spectrally sensitised photo polymerisable material useful in systems for data recording and for producing printing plates, printed circuits, photocurable adhesives and surface coatings. The material has high sensitivity to near UV and short wavelength visible light in the 310-420 nm range. The material has an initiator system comprising certain light-absorbing 1,4-dihydropyridines having electron-withdrawing substituents (ester, acid, ketone, amide or nitrile groups) at the 3- and 5-positions, and one of a range of onium salts which include iodonium and sulfonium salts. It is known that electron-withdrawing substituents capable of resonance interaction in the 3- and 5-positions stabilize 1,4-dihydropyridines by extending the conjugation ("THE CHEMISTRY OF DIHYDROPYRIDINES" by Ulli Eisner and Josef Kuthan in Chemical Reviews, Vol. 72, No. 1, 1972, pages 1-42 at page 3). Such stabilised 1,4-dihydropyridines would not be reactive with oxygen and it is noteworthy that the specification makes no reference to any involvement of air in the initiation of polymerisation. Therefore DD 287,796 A6 contains no teaching about air-activatable compositions but depends upon the stability and light-absorbing characteristics of the particular 1,4-dihydropyridines disclosed therein.
It is the object of the present invention to provide a one component substrate-insensitive polymerisable composition which is stable on storage in the absence of air, which is activated by exposure to air (without requiring photo-activation) and which then cures in either the presence or absence of air, but which does not require the presence of a weak acid for satisfactory auto-oxidation performance.
It is an object of this invention to provide an air-activatable composition which does not require photo initiation.